Atomic reactor



Nov. 7, 1961 c. E. sTooPs ETAL 3,007,859

ATOMIC REACTOR 3 Sheets-Sheet 2 Filed Aug. 15. 1956 INVENTRS J. M DAY C.E. STOOPS BY Z lll IIIIHI' L, 77

A 7' TORNEKS' Nov. 7, 1961 c. E. sTooPs ETAL 3,007,859

ATOMIC REACTOR Filed Aug. l5. 1956 62 M eo -YW [es 3 Sheets-Sheet 5GAMMA INTENSITY, R/hr. 0| 0 O 2O 40 60 8O kIOO |20 |40 DECAY TIME, DAYSINVENTORS J. M. DAY C. E. STOOPS mma-v A 7` TORNEVS 3,@9559 PatentedNov. 7, 196i free ATQMIC REACTGR Charles E. Stoops and James M. Day,Bartlesville, Okla.,

assignors to Phillips Petroleum Company, a corporation of Delaware FiledAug. 15, 1956, Ser. No. 604,269 2 Claims. (Cl. 2ML-193.2)

This invention relates to novel atomic reactor construction. A specificaspect of the invention pertaining to the irradiation of liquidhydrocarbons and, particularly, lube oils and lube oil stocks isdisclosed and claimed in our Iapplication S.N. 1,529, filed January 1l,1960.

We have found a simplified atomic reactor construction which eliminatesthe conventional machined graphite blocks and graphite pebblessurrounding the active lattice of an atomic reactor. This isaccomplished by utilizing a refined hydrocarbon oil as a moderatorsurrounding the tank in which the active lattice is positioned. We havealso found that by subjecting certain lube oils to gamma radiationeither in the area surrounding the lattice of a reactor or in the areaadjacent the spent fuel elements from a nuclear reactor, a favorabledecolorization of the lube oil is effected.

Accordingly, it is an object of the invention to provide a novel atomicreactor. Another object is to provide a process for irradiating certainhydrocarbon lube oils and lube oil stocks. Other objects of theinvention will become apparent upon consideration of the accompanyingdisclosure.

The development of atomic energy has resulted in the development ofterminology peculiar to this particular field. In order to facilitatethe understanding of the invention it is desirable to discuss andclarify some of the terms which are particularly applicable to theatomic energy field. The term reactor is applied to the physical meanswhereby a critical amount of radioactive material is positioned,inclosed, supported and shielded so as to be self-sustaining, i.e., theradioactive material and the environs return as many thermal neutronsper unit of time to the reactor core as are needed to produce the numberof fissions per unit time from which the-y originally came. Obviouslyexcess reactivity must exist in order to produce useful energy for areasonably long period of time. This excess reactivity is controlled andintroduced as fuel is burned by means of control rods.

The term fuel in an atomic reactor includes any of the heavy elementswhich are capable of undergoing the lission reaction.

Moderators are used so that the neutrons given up by the fissionreaction in the fuel core as high energy or fast neutrons, may be sloweddown and thereby reduced in energy to the so-called thermal or slowneutron range of energies. This is brought about by elastic collisionwith :the atoms of the moderator, and each elastic collision removes aportion of the energy from the neutron in the form of kinetic energyimparted to the molecules of the moderator and which will eventuallyshow up as heat. The best moderato-rs are th-ose having a low capturecross section, low atomic weight and relatively high scatter n crosssection, that is they are capable of under-going many elastic collisionsand of serving as a medium for neutron diffusion without capturing aneutron in the nucleus. Moderators may be liquids, solids, or gases.However, the Ilater form lacks sucient density to be highly effectiveexcept at extreme pressures or with infinite space.

A reflector is a blanket of moderating material, surrounding the fuelcore (consisting of fuel, moderator, coolant, and such structuralmaterial as necessary) which, by moderating and returning neutrons tothe fuel ocre reduces the lamount of fuel necessary for the reactor tosupport a self-sustaining fission reaction. It also serves as areservoir of neutrons that can be used for useful purposes, such as theproduction of radioactive isotopes. In general, moderators andreflectors have the same requirements.

The properties which are necessary and desirable in a moderator are suchthat hydrogen, carbon, or compounds thereof qualify exceedingly well.None of these will be appreciably activated by irradiation and all havelow atomic mass and tend to be very efficient in the absorption ofenergy from an energetic neutron. They also have a high scattercross-section so that collisions are frequent.

This suggests that organic materials, particularly hydrocarbons, wouldbe good moderating materials. A liquid hydrocarbon material can be usedas a coolant as well as a moderator and serve a double purpose.

Although it is impossible in a reasonable length of time rto discuss allthe ramifications in the choice of moderators and moderator-coolants,the advantages of the use of organic materials are sufficiently obviousto those familiar with the ant that the Atomic Energy Commission isexpending a large sum of money on an experimental organic moderatedreactor. Such an expensive experiment is necessary because of problemsstemming largely from the thermal and radiation instability of organicmaterials in general. A good discussion of some of the advantages oforganic moderators and the instability problem and a summary of theAtomic Energy Commission supported laboratory investigations is given byR. G. Bolt and I. G. Carroll (Proceedings of the InternationalConference on the Peaceful Uses of Atomic Energy, vol. 7, 546-555 (1956)It is necessary to know the stabilities of many organic materials and todevelop techniques for purifying those which are suflciently stable touse. The latter is necessary because no organic material is completelystable to radiation; the most promising so far have been large aro-maticmolecules, such as polyphenyls and fused ring aromatics.

Advantages of our invention are that it substitutes relativelyinexpensive lubricating oil for these expensive chemicals and eliminatesthe costly purification processes necessary to maintain these materialsin a suitable state of purity. In addition, in the course of acting as amoderator and/or coolant, the oil is improved and p-rocessed to a moreuseful product. The lubricating oil can Ireplace all of the moderating,cooling, and reflecting marterials or, alternatively, only one or two ofthese functions may be served. It is important for economic reasons thattemperatures be maintained below the boiling point of the lubricatingoil. Operation at atmospheric pressure is thereby possible withconsequent lighter construction permissible. It is also preferable tomaintain atmospheric pressure in the reactor because of the possibleescape of radioactive gases when super atmospheric pressures areemployed.

Atomic reactors may be divided into many categories for purposes ofdiscussion. One means of classification is based on the configuration ofthe fuel elements in the reactor core. Such terms as homogeneous,heterogeneous, and fluidized, are typical examples. By homogeneousreactor one denotes a reactor in which the radioactive fuel is insolution in a moderating liquid. In heterogeneous reactors, the fuel ismore or less in lumps, clusters of rods and such configurationsseparated by solid or liquid modifiers. Fluidized reactors, as the namesuggests, indicates a reactor in which small par ticles of moderatedfuel are fluidized by non-neutron absorbing gas such as helium and thelike. This type of reactor is in the experimental stage and little moreinformation is available. Another classification deals with the type ofmoderator used, thus we have terms such as light water, heavy water,graphite, and organic, to

describe moderated reactors in each of the above fuel configurationcategories. Another type of classication relates to the particular typeof fuel element used. Examples are natural uranium, enriched uranium,thorium, and plutonium. Occasionally, such terms as swimming pool andwater boiler are used as further means of identification. These termsrefer to similarity of the reactor to well-known structures andphenomena. Another means of identification is based on the luse of thereactors, such as power reactors, test reactors, and breeder reactors.Breeder reactors are those in which as much or more nuclear fuel isproduced as consumed.

Within the reactor core, the lissioning fuel constantly gives olf fastneutrons, gamma rays, and radioactive lission products. The fastneutrons, the prompt gamma rays from the fission process, Vand the gammaand beta rays from the radioactive fission products are collectivelyknown as ionizing radiation because directly or indirectly in theirpassage through matter their energy is dissipated by the formation ofion pairs and activated molecules. These ion pairs and activatedmolecules are responsible for the chemical effects that lead to thedegradation of organic compounds. The term ionizing radiation valsoincludes high energy ionic particles such as protons, deutrons, alphaparticles, etc. which are not of primary importance in a discussion ofreactors, but which might be of importance in the treatment of organiccompounds such as lubricating oils. The high energy fission fragments,themselves, are ionizing radiation but are usually retained in the fuelalloy and hence have no effect on the moderator.

The present invention utilizes `a hydrocarbon oil asV themoderator-reflector, as a portion of the moderator, or as a portion ofthe reflector in any of the experimentally proven reactors. This ispossible because of the low capture cross-section of both the carbon andhydrogen atoms present in the hydrocarbon oil. Graphite, which is purecarbon, is an exceptionally good moderating and reflecting material andhydrogen under high pressure or at low temperatures would also be anexcellent moderator or reflector. However, both conditions necessary forits use are extremely difficult to obtain in the reactors underdiscussion. However, when combined with carbon in the form ofhydrocarbons, as in this invention, the resulting material possesses thedesirable properties of both carbon and hydrogen and has the advantagethat it is a liquid and lends itself to the shape of the container atnormal temperatures or pressure, whereas carbon must be shaped byexpensive machine methods and the hydrogen properties as noted above arecompletely outside the realm of consideration. The invention alsocomprises improving the color characteristics of a lube oil bysubjecting the oil to gamma radiation from `a reactor or spent fuel, orother ionizing radiation.

In order to provide a more complete understanding of the inventionreference is made to the schematic drawings of which FIGURE 1 shows avertical cross-section of a reactor embodying the invention. Y

FIGURE 2 is a schematic cross-section of a reactor canal with storagefacilities and handling facilities in which it is convenient to exposelube oil to the gamma radiation from spent fuel elements.

FIGURE 3 shows a fuelV assembly similar to those used in the MaterialsTesting Reactor (MTR) operated for the Atomic Energy Commission, at TheMaterials fuel element versus an assembly of eight spent fuel elementsarranged as in FIGURE 5.

Referring to FIGURE 1, reactor 10 comprises a central tank 12 closednear the upper end by a lead partition 14 including a lead plug 16.Partition 14 provides a shielded operating room 18 above reactor fuelcore 20 which is controlled by means of control rod 22 from room 18..

this compartment. Reflector compartment 26 is encased in and completelysurrounded by a concrete shield 28. In one embodiment of the inventioncompartment 26 and tank 12 (below partition 14) are lled with ylube oiland conduits 30 and 32 4are connected with the lower and Y upper ends ofcompartment 26 for 4introducing and removing oil respectively, to andfrom, compartment Z6. Control of oil flow is effected by remoteoperation of valves 34 and 36. Valve 38 and conduit 4l) provideV oilcirculation means thru tank 12 around fuel core 20.

Conduits 30 and 32 are connected to a lube oil storage tank 42 by meansof valved conduits 44 and 46. A conduit 48 provided with a pump 50circulates toil from the storage tank -thru the reactor compartments andback to tank 42. Lube oil of improved characteristics may be drawn offas desired thru valved conduit 52.

A fluid turbine operated electrical generator 31, having leads 33, isconnected by fluid conduits 3'5 and 37 to an indirect heat exchanger 39which in turn is connected Y with oil line 32 by means of conduits 41and v43 so as Testine Reactor, National Reactor Testing Station, Idaho.

FIGURE 4 is a crossfsection on the line 4--4 of FIG- URE 3 with fuelplates in place. Y

. FIGURE 5 shows a partial plan view of a Storage r-ack for spent fuelelements located in the reactor canal of FIGURE 2. Y

FIGURE 6 is a longitudinal cross-section of the irradiation containerused in our study of the effects of ionizing radiation on lube oils.

FIGURE 7 is a decay curve for single spent MTR to provide heat exchangewith the hot oil and fluid power for the turbine of generator 31. It isalso feasible to supply uid power from heat exchange within tanks 12 or26. Y

FIGURE 2 shows an elevation partially in section of a canel 54positioned below a reactor for storage of spent fuel assemblies 56 inracks 58. Fuel elements are delivered to the canal by means of a chute60 which connects (by means not shown) with fuel core 20. A crane 62which is operated from a tunnel `adjacent wall 63, is provided fortransporting fuel elements in the 16 to 18 feet of water in canal 54.

FIGURE 3 showsV the shell of an MTR type fuel assembly. The shell 64 ismade of aluminum plate with Y two flat sides 66 and 67 `and two curvedsides 68 and 69 (sho-wn in FIGURE 4). End sections 71 and 72 are rivetedand welded to the fuel section 73 t-o provide a cylindrical upperterminal 74 adapted to lit holes in a. grid (not shown) in fuel core 20and to provide a square terminal section 77 to lit in holes 78 of alower grid (not shown). A spring 79 is provided on cylindrical terminal74 to compensate for vibrations arising during the operation of thereactor.

Referring to FIGURE 4, the fuel plates 81 are shown brazed to groovesprovided in straight sides 66 and 67 of the shell 64. The curvature andspacing of the fuel platesl are further maintained by means of aluminumcones 82 which are brazed to the pla-tes near eachend. In the fuelelements shown in FIGURE 4, 18 fuel plates are utilized on a 0.117 inchspacing. The fuel plates per se are made'of aluminum-uranium alloy. Theuranium in the alloy contains 168 grams of U235 per assembly.

The uranium-aluminum alloy is incapsula-ted in an aluminum-casing tomake up the fuel'plates which are approximately 0.06 inch thick. v When27 of the fuel assemblies are positioned in a 3 x 9 arrangement, thereactor will produce 30,000 kw. of energyufor a period of; 20 dayswithout refueling.

FIGURE 5y shows a plain viewV of a portion of a canal storagerack 58including an array of 8 fuel elements F in rectangular geometry withrespect to the center lineV of space 84.

FIGURE 6 shows an irradiation container suitable for enclosing liquidand gaseous materials to be inserted in an active eld of a reactor. Thecontainer comprises a closed aluminum body 86 and Aa steel end plug 88sealed to the body by lead gasket 89. The upper closure comprises abrass valve and shutoff plug 9i) extending thru a brass packing nut 9ithreaded into body S6. A rubber Oring 92 seals the top closure with body86. A brass carrying nut 93 to which an eye g4 is attached providesmeans for attaching to a conventional positioning device. Gas may beremoved from or injecte into the container thru channels 9S and 96 byremoving carrying nut 93 and `by backing valve @if its seat. When thevalve is used for evacuating or admitting gas before irradiation or forremoval of gas for analysis after irradiation, the rubber O-ring is putin place to seal on the gas path. This O- ring is removed beforeirradiation and replaced afterward.

When the spent fuel assemblies are removed from the reactor, they have avery high gamma radiation coming mainly from the decay of fissionproducts and when immersed in Water the gamma radiation from a singlefuel element, measured at a point l centimeters from the fuel element,shows an initial gamma intensity of 3 X 10G r. per hour and decays to105 r. per hour in approximately 120 days. This is illustrated in FIGURE7 which is self-explanatory. Curve I is the decay diagram for spent fuelelements stored in the canal as shown in FIGURE 5 in a rectangular arraymade up of 8 spent fuel elements. On the center line of space 84, theinitial gamma intensity is l07 r. per hour which decays in about 20 daysto 3 l043 r. per hour. At that time, another group of spent fuelelements is removed from the reactor and upon replacing the originalspent fuel elements, the intensity is again raised to 107 r. per hour sothat gamma intensity in the range l07 to 3 l06 r. per hour is readilyavailable on a continuous basis during the normal operation of a reactorsuch as the MTR.

Preliminary to a detailed description of a specic example relating toirradiation of lubricating oil, a discussion of lubricating oils will behelpful and, in particular, the preparation of the lubricating oil whichis the subject of the specific irradiation of the invention.

Lubricating oils from petroleum are predominantly of high (350-800 orhigher) molecular weight. The various types may be named in accordancewith the type of crude from which they originate. West Coast,Mid-Continent, and Pennsylvania designate the three major types found inthe United States. Pennsylvania crude is predominantly paratlinic incharacter, Mid-Continent is predominantly asphaltic in character and theWest Coast is even more asphaltic with the added cha-ractor of havingconsiderable amounts of non-hydrocarbon impurities containing sulfur andnitrogen. After careful examination of a Mid- Continent crude, the U.S.Bureau of Standards drew the conclusion that the lube oil fraction ismade up of 4,000 n constituents. This is Ibased on laboriousdistillations made at the Bureau of Standards Laboratory wherein thelube oil was cut up into 4,000 fractions having different properties andeach fraction comprising more than one constituent. It is believed thatthe factor n is probably a small number greater than one, although itsmagnitude has not been established. From their findings, it is believedthat attempts to speak of lubricating oils in other than very broadterminology is futile.

For good lubricating properties in modern motor cars, an oil must haveproper viscosity and high viscosity index. It has been found that theseproperties are present in fractions composed predominantly of compoundscontaining a naphthenic nucleus with long paraiiinic side chains. T-hemore asphaltic crudes trend toward mixed naphthenicaromatic nuclei. Longparalinic side chains mask the effects of the aromatics when measuringsuch properties as viscosity index and pour point; however naturalformation of the constituents in crude oils appears to favor ringformation at the expense of side chains; and accordingly,

6 the asphaltic crudes contain multi-ring nuclei having varying degreesof unsaturation.

Solvent extraction has largely replaced fractionation for the nalseparation and preparation of lubricating oil base stocks Ifrom crude.The solvents utilized are usually selective for the more aromatic orunsaturated hydrocarbons and therefore yield a raffinate phase richer inthe parainic and naphthenic stocks, which have desirable lubricating oilproperties. As pointed out above, long paranic side chains are capableof masking unsaturation; and accordingly, small amounts of unsaturates(aromatic and/or olefinic) are present in lubricating oil base stocks.These compounds are one of the causes of color observed in lubricatingoils and may along With related impurities be responsible for the bloom(green fluorescence) of lubricating oil stocks.

As an example of the process utilized in preparing the feed stock ofthis specific example, a description will now be given for thepreparation of SAE 250 lubricating oil base stock from a Mid-Continentcrude. After an original flashing, de-salting, and de-emulsiiication ofthe raw crude stock, the material is charged to a topping still whereingasoline and light gas oils are removed therefrom. The residue is vacuumdistilled to remove heavy gas oil and light lubricating oils of SAE 10viscosity and SAE 20 viscosity grades. The residue is then subjected tofractionation in the presence of propane to take overhead a fractionhaving SUS at 210 F viscosity, and also a second fraction having aviscosity of about 200 SUS at 210 F. The latter fraction is phenolextracted to produce a less aromatic ranate which is propane de-Waxed toproduce a 250 SAE lubricating oil base stock.

A portion of this lube oil base stock was placed in the B-typeirradiation container shown in FIGURE 6. The container was loweredthrough the Water in the canal at the MTR gamma facility into the centerof an array of spent fuel elements such as shown in FIGURE 5. Threesamples were utilized in order to determine the effect of variousdosages of gamma radiation. The iirst dosage required approximately 10minutes in the gamma facility to obtain a dosage of 106 r. units. Asecond portion was irradiated one hour to obtain a dosage of 107 r.units and a third portion was irradiated for l0 hours to obtain a dosageof 108 r. units. The following data were obtained on the samples beforeand after irradiation.

Irradiation Dose Unirra- 10 rep 1 107 rep 1 l09 rep 1 diated API Color(NPA) Carbon Residue 1 Rep (Roentgen equivalent physical) is a unit formeasuring dosage and represents an absorption of radiant energy of 93ergs por gram.

These results show that lubricating oils are very little affected, otherthan by color improvement, by high gamma flux such as is encountered inhigh energy atomic reactors similar to the MTR. They are also highlyresistant to the absorption of neutrons at all energy levels encounteredin all known types of atomic reactors. Therefore, the present inventioncomprises not only the improvement in color of lubricating oils byirradiating same in a gamma facility, lbut also the use of such highlyunreactive hydrocarbons in the moderating and reflecting zones of atomicreactors to take advantage of their versatility as moderators andcooling agents. T o take the example of the MTR reactor, the use oflubricatingoils in the permanent graphite section is advantageousbecause expensive machining of the graphite blocks is eliminated and nosuch costly purification, as required in preparing the graphite toremove traces of boron (which represents the predominant part of thecost of the raw graphiteused` they are already completely purified andare free ofV poisons In utilizing lubricating oils as coolant in thetank section, the reactor is preferably designed to operate atrelatively low temperatures although temperatures as high as 700 to 900F. can be tolerated because lubricating oils are made to operate undersuch conditions and have been tailored to contain only highly refractoryhydrocarbon types. It is preferred to operate under temperatureconditions wherein the lube oil does not become heated to over 700 F.but temperatures as high as 900 F. can be tolerated where the oil iscirculated thru the reactor without excessive residence time therein. In`fractionating a 250 Kansas City base stock at 925 F. it was found thata first fraction representing less than 10% of the base stock wasobtained.

Certain modications of the invention will become apparent to thoseskilled in the art and the illustrative details disclosed are not to beconstrued as imposing unnecessary limitations on the invention.

We claim:

1. An atomic reactor capable of producing power comprising an innerenclosed chamber adapted to maintain a high temperature above 212 F.including a ission-sustaining lattice containing ssionable material, amoderator coolant comprising lube oil, and means for converting the heatin said moderator coolant to electrical energy; -an outer enclosedchamber containing a lube oil; a lube oil storage tank; conduit meansconnecting the lower sections of said inner and outer chambers with saidYstorage tank; conduit means connecting the upper sections of said innerand outer chambers with said storage tank; and a protective radiationshield enclosing said chambers.

2. An atomic reactor comprising a tank lled with a lube oil moderator; aiission-sustaining lattice containing ssionable material in said tanksurrounded by said lube oil; a storage vessel for lube oil; acompartment illed with lube oil surrounding said tank; Valved conduitmeans connecting the lower sections of said tank and said compartmentwith said vessel; valved conduit means connecting the upper sections ofsaid tank and said compartment with said vessel; and a protectiveradiation shield surrounding said tank and compartment.

References Cited in the tile of this patent UNITED STATES PATENTS OTHERREFERENCES KAPL-731, AEC Document dated Apr. 2, 1952; pages 3 and 5.

1. AN ATOMIC REACTOR CAPABLE OF PRODUCING POWER COMPRISING AN INNERENCLOSED CHAMBER ADAPTED TO MAINTAIN A HIGH TEMPERATURE ABOVE 212*F.INCLUDING A FISSION-SUSTAINING LATTICE CONTAINING FISSIONABLE MATERIAL,A MODERATOR COOLANT COMPRISING LUBE OIL, AND MEANS FOR CONVERTING THEHEAT IN SAID MODERATOR COOLANT TO ELECTRICAL ENERGY, AN OUTER ENCLOSEDCHAMBER CONTAINING A LUBE OIL, A LUBE OIL STORAGE TANK, CONDUIT MEANSCONNECTING THE LOWER SECTIONS OF SAID INNER AND OUTER CHAMBERS WITH SAIDSTORAGE TANK, CONDUIT MEANS CONNECTING THE UPPER SECTIONS OF SAID INNERAND OUTER CHAMBERS WITH SAID STORAGE TANK, AND A PROTECTIVE RADIATIONSHIELD ENCLOSING SAID CHAMBERS.